Method of and apparatus for producing zinc oxide



Jan. 19, 1932. H. REINHARD 1,842,287

METHOD OF AND APPARATUS-FOR PRODUCING zinc OXIDE Filed June 25, 1929 IA! &\\\\\\\\\\\\\\l' INVENTOR.

By W

jjkrcwg A TTORNEYJ.

. Patented 'Jan. 19, 1932 ,UNI'HED srnrss PATENT? Fl lt'irl HUGO REINI-IARD, OF OBEBHAUSEN,GERMANY METHOD or AND APPARATUS non rnonuo ne zmo oxrnn Application filed. J'une 25, 1929, Serial No. 373,589, and in Germany and. in the Netherlands December 3, 1923.

This invention relates to an improved and process for the manufacture of simplified (zinc white) from zinc (refined zinc oxide zinc, ordinary spelter, remelted zinc, zinc ejdross) or from mixtures capable of producing zinc vapor by distillation or reduction, whichvapor is subsequently burned to form oxide of zinc. More particularly the object ,of the invention is the elimination of a source of loss inherent to the old method of manufacture and a simultaneous improvement in the productlon of hlgh grade zlnc whlte.

It is well known that when zinc is evapo- .rated in the usual manner in a muffle or similar (e. g. electrothermic) furnace, the zinc vapors issuing from the outlet-hole of thevaporizing apparatus produce a depos t which formsaround said outlet, th1s deposit .or accretion growing and thereby developing into tubular or horn-shaped bodies. The

origin of these accretions may be explained by partial condensation of the zinc vapor around the edge of the outlet-hole and subse- .quent combustion of the deposited zinc dust and globules of zinc embedded therein to solid oxide of zinc of a verylow grade.

In the case of the exit of the zinc vapor in a substantially horizontal direction (through an outlet opening in a substantial-v, 39 'ly vertical Wall of the distilling vessel) to which the present invention particularly re fers, at first a lip-shaped or cup-shaped deposit is formed at the underside of the vapor .outlet, which deposit in a comparatively short time develops into a tubular body around the outlet and protruding from the said outlet, presumably owing to the interaction of condensation and oxidation.

This body gradually assumes considerable 40 size and various shapes generally growing the direction of the flow of the vapor, gradually closing up and thusobstruoting the exit of said vapor outlet unless the accretions are stripped off or otherwise removed in proper time. The constant removal or stripping off requires expensive and troublesome hand work. Moreover these accretions (being waste or low grade products) considerably I reduce the yield of first grade zinc oxide and have to be retreated by a separate process.

I have now discovered that it is possible not only to suppress the formation of these wasteful accretions but also to enhance the quality of the regular product (zinc white of superior grade) by a very simple and efzinc vapor which will issue as a substantially horizontal current)-in such a manner that the flame creeps up and isspread out upon that part of said vertical wall which is located underneath the vapor outlet thus contacting with the (horizontally) issuing jet of zinc vapor in a plane substantially perpendicular to the direction of flow of the zinc vapor, at the exit opening. It has proved most convenient and effective to feed a (combustible) gas by means of a suitable distributing or spreading device against the wall allowing the (flattened) stream of gas to ignite while contacting with the surface of the said wall on the one side and the surround ing air on the other side. It will thus burn consumes the oxygen from the surrounding air otherwise apt to burn the (condensed) zinc to solid oxide. flame tends to superheat the zinc vapor and thereby to raise its temperature of combustion. To this hot combustion of the zinc vapor the inventor largely attributes the marked improvement in the quality of the zinc white produced upon applying the present process.

It isquite important that the flattened stream of gas fed against the vertical retort wall underneath the outlet hole of the zinc vapor, should ascend along the wall with only a moderate velocity so as not to disturb or On the other hand the deviate to any considerable extent the (horizontal) exit of the zinc vapor fro-m the exit opening, the velocity of the latter being generally such as to keep up the horizontal flow for a certain distance (say about 4 inches) before being deflected upwardly to any considerable extent owing to the buoyant effect of the hot burning zinc vapor. 7

Que mode of carrying out the invention will now be described more in detail in connection with the annexed drawings which shows a suitable apparatus for carrying out the process, but the invention is not limited to this apparatus shown by way of example' Fig. 1 represents a partial vertical section through a suitable distilling vessel or retort and a convenient device for leading the gas flame from below to the outlet opening of the vessel and also showing a part of the flue leading intothe settling chamber, while Fig. 2 shows an end view of the vessel, also showin the gas distributing device. Like numerals denote correspondingparts in both figures.

1 represents part of the distilling vessel or retort containing the material (molten zinc or other material from which zinc is to be distilled in the form of vapor) which vessel may be heated externally (e. g. by means of gas) or internally (e. g. by electrothermic devices not shown in the figure) as desired or customary. 2 shows the vertical (end) wall of the said vessel, containing the exit opening 3 for the zinc vapor 'V,which issues as substantially horizontal (or perhaps sli htly inclined) stream. This opening 8 is lined with an annular casing or ring 4 of suflicient.

1y refractory and mechanically resisting material (e. g. carborundum or mixtures of the same with fire-clay and the like) provided for giving the exit hole a. regular and permanent (preferably circular) shape. 5 is a pipe connected to any suitable supply of combustible gas (not shown in the figure) the pipe 5 is provided with a spreading device 6, of approximately triangular shape, with side flanges resting against the vertical wall 2 of the distilling vessel 1 This device 6 may be constructed preferably of special iron or other heat-resisting material, which is adapt ed to flatten the stream of combustible 7, issuing from the pipe 5 and to feed it as a fan-shaped, upwardly flowing stream, following the wall 2-, by which it is guided upwardly, to the vapor outlet. as indicated by the arrows at 7 in l and 2.

It is to be noted that there are no cold metal parts or other solid surfaces in front of or close to the vapor outlet 3, of the retort, or in or close to the path of the flame of the zinc oxide, as will clearly appear from the drawings. Such surfaces, if present at the position indicated would soon be covered by a coating of relatively hard incompletely oxidized zinc oxide and zinc, and would have to be cleaned frequently.

This distributing device obviously serves also for protecting the orifice of the feeding pipe 5 from choking or clogging by pieces of oxide or the like falling down into the same from the outlet.

I again call attention to the fact that the gas is not blown out of the top of the spreader 6 as a forceful rapid stream, but the gas flows out a gentle stream. Hence the gas stream or gas flame, does not materially swerve or blow the stream of burning zinc oxide from its natural substantially horizontal direction. Also the gas flame, or the burning gas 7, tends to completely encircle the base of the jet of zinc vapor coming from the opening 3, to protect all parts of the ring l from the formation of a crust of zinc oxide thereupon.

8 represents a flue or passage leading into a hot chamber, settling chamber, bag filter, electrostatic precipitator or other device or devices for collecting the Zinc oxide. 9 is a manhole or door for gaining access tothe end of the retort, gas distributor, for replacing the retorts and spreaders, cleaning, etc.

The means hereinbefore described for feeding the protective gas from underneath to the rooosed b others is a decisive improve- L r J ment, as regards the practicability of the process, for it is of utmost importance that the stream of protective gas should interfere as little as possible with the ordinary flow of the zinc vapor. Annular nozzles will. necessarily have to be operated with relatively high pressure thereby likely to cause disturbances in the cutflowing zinc vapor, otherwise they are subject to choking or clogging by accretions, and to rapid destruction by the heat and zinc vapor.

While the gas-supply device described and illustrated. by the drawings has been found to be of utmost simplicity and convenience and least liable to trouble from clogging or corrosion (owing to its vertical distance from the zinc flame) the invention is obviously not limited to this special form of adducing the gas flame from underneath and sideways to the issuing jet of zinc vapor. The spreading device may be replaced by any suitable spreader mounted upon the feeding pipe, the orifice of the feedingpipe itself may be flattened to a slot and covered with a distributing plate or the like or the flattened stream of burning gas may be produced by several feeding devices of the kind described or other suitable design without departing from the gist of the invention.

As has been stated above the application of a combustible gas burning with a reducing flame in the process hereinbefore described offers specific advantages over other (noncombustible or inert) gases. But the mode of feeding gas to the vapor outlet peculiar to my invention is not limited to a particular kind of combustible gas. Thus good producer gas, illuminating gas, coke-oven gas, have been found satisfactory.

The gas should be of high calorific value and preferably high in carbon monoxide but relatively low in hydrogen.

In carrying out the process of this present invention, it is essential to employ a readily combustible gas, to get the best results. Tests have been conducted, using an inert gas (nitrogen), fed in the same manner, but no real measure of success could be attained thereby although the amount of accretions formed was materially reduced. Such inert gas also would be objectionable on account of the coolmg effect on the zinc vapor. It is necessary to preserve the heat in the zinc vapor, and

preferable to increase the heat by theburn- 111g gas.

It 1s therefore necessary not to place any obstructing devices at the exit side of the re-' tort, close to the vapor outlet, since such devices would serve as points on which the crusts would soon collect.

It may be noted that in actual practice of the zinc white manufacture, it is the custom p0 heat the retorts to about 1300 C., more or ess. 1

In the usual old practice it is advisable to clean the outlet openings of the retorts,

often as every three minutes, to keep them fairly clean. This is usually done by hand, with scraping irons, chisels, etc. In experiments in which inert gas was used with the appliances shown herein, it was still advisable to clean the vapor outlets of the retorts, as often as every ten or fifteen minutes. In another case, air was fed by pipe 5 and di tributor 6, to the zinc vapor stream. Here no improvement could be observed over the ordinary practice. With my process, cleaning every hour or two is suflicient.

The use of inert gas or air, also did not improve the quality of the zinc white product. While 'my process gives a very high grade zinc oxide, without anyneed of reheating,

e the zinc oxide produced when using inert or air, must be recalcined to completely oxidize the particles of zinc left in it, as in the customary old practice. This is unnecessary when carrying out the present process, very fine flulfy brilliant White zinc oxide, of the highest covering power (for paints) being collected directly.

The present case is in part a continuation of. m copending application filed Nov. 525, 1924, Serial No. 752,267.

I claim 2- 1. An improved process for the manufacture of high grade zinc oxide from metallic zinc or zinc producing mixtures, while avoiding losses and disturbances due to the formasome distance below thevapor jet and the wall of the distilling vessel serving as a guiding surface for the gas and flame to the superposed exit opening in said vertical wall, from which the zincvapor issues in a substantially horizontal direction.

' 2. An improved process for the manufacture of high grade zinc oxide from metallic zinc or zinc producing mixtures, while avoiding losses and disturbances due to the formation of accretions of solid zinciferous material at or near the exit opening of the distilling vessel, consisting essentially in feeding a gentle stream of burning combustible gas to the outside ofa substantially vertical wall of the distilling vessel, and close to the exit opening in said vertical wall, from which the zinc vapor issues in a substantially horizontal direction, said vertical wall acting as asurfaoe for guiding said stream of burning gas, said gentle gas stream meeting the zinc vapor stream substantially perpendicular retort, and feeding a gentle stream of a burning combustible gas containing CO and of high calorific value directly to the outside of the outlet opening of the retort, by a gas conduit which terminates near said outlet, and allowing free combustion of the zinc vapor and of the combustible gas so fed in, and collecting the zinc oxide formed, said combustible gas meeting the issuing zinc vapor substantially perpendicular thereto.

l. A process as in claim 1, in which the gas is delivered against the retort wall, as a flattened stream, with only a gentle flow.

5. A process for producing high grade zinc oxide from zinc metal or zinc-containing mixtures by volatilization of zinc in a vaporizing vessel and subsequent combustion of zinc vapors issuing in a substantially horizontal directionfrom a lateral outlet of the vaporizing vessel, comprising the step of feeding a gentle reducing flame of combustible gas from underneath and substantially perpendicular to the susbtantially horizontally issuing jet of zinc vapor, and adjacent to said lateral outlet, for the purpose of preventing the formation of metallic or oxidic accretions at said outlet.

6. In an apparatus for the production of tort, a zinc retort having a substantially Vertical end wall provided with a vapor outlet, and an oxidizing chamber into Which the zinc vapor is directly discharged from said vapor outlet of the retort, the outside of said vapor outlet being wholly unobstructed; in combination with means for delivering a reducing flame upwardly along the said vertical end wall of said retort, said means being situated somewhat below the vapor outlet of said retort and within said oxidizing chamber.

In testimony whereof I aflix my signature.

HUGO REINHARD. 

